1. Field of the Invention
This invention generally relates to wireless communications antennas and, more particularly, to a tri-band antenna that resonates at three non-harmonically related frequencies.
2. Description of the Related Art
The size of wireless communications devices, such as wireless telephones, continues to shrink, even as users demand more functionality. One consequence of this tension between size and function is the pressure for manufactures to make smaller antennas. This pressure is compounded if the wireless device is expected to operate in a plurality of frequency ranges. Many wireless telephones, for example, are expected to operate in the cellular band of 824 to 894 megahertz (MHz), the PCS band of 1850 to 1990 MHz, and to receive global positioning satellite (GPS) signals in the band of 1565 to 1585 MHz. Other telephonic devices are also expected to operate in the Bluetooth band of 2400 to 2480 MHz.
Conventionally, each wireless device transceiver or receiver is connected to a discrete antenna that resonates at the operating frequency of the transceiver. However, it is difficult to locate so many antennas in a small wireless device telephone. Therefore, antennas have been developed that operate at more than one, non-harmonically related frequency. For example, it is known to combine two non-harmonically related resonant frequency responses into a small microstrip antenna formed on two sides of a dielectric. Such a design is inadequate to cover three frequency bands, however. One work-around solution for the above-mentioned antenna has been to widen the bandpass response of in the higher frequency band, to cover GPS and PCS communications for example, and to use the lower frequency band to resonate at cellular band (AMPS) frequencies. However, the widening of the higher band, to improve GPS and PCS performance, comes at the expense of cellular band performance.
It would be advantageous if a small microstrip antenna could be designed to resonate at three distinct non-harmonically related frequencies.
It would be advantageous if the above-mentioned microstrip antenna could be designed to operate in the cellular, GPS, and PCS bands.
The present invention describes a microstrip design antenna that resonates at three discrete, non-harmonically related frequencies. An example is given of an antenna that resonates in the frequency bands of 824 to 894 MHz, 1565 to 1585 MHz, and 1850 to 1990 MHz. This antenna has the further advantage of being very small and, therefore, useable with a portable wireless device or laptop computer.
Accordingly, a tri-band antenna is provided comprising a meander line radiator, a tapered line radiator, a straight line radiator, and a dielectric layer having top surface and a bottom surface. Each dielectric layer surface has an area of less than 1.0xc3x97106 square mils (mils2). The meander line, tapered line, and straight line radiators are formed as microstrip structures overlying the dielectric layer top and bottom surfaces.
More specifically, the meander line radiator is formed on the dielectric top surface and has an input connected to a transmission line feed. The meander line is connected to the tapered line radiator on the dielectric bottom surface through a via. The straight line radiator is connected to the tapered line radiator output on the bottom surface, and is unterminated.
In one aspect, the combination of the meander line radiator, tapered radiator, and straight line radiator forms a first effective electrical length corresponding to the cellular frequency band, a second effective electrical length corresponding to the GPS frequency band, and a third effective electrical length corresponding to the PCS frequency band.
Additional details of the above-described tri-band antenna, and a method for forming a tri-band electromagnetic radiator are provided below.